Electron gun



Feb. 12, 1952 J. R. PIERCE 2,585,582

ELECTRON GUN Filed July 7, 1949 F/GJ Fl6.5 6 as'aa 52h .aa'

"6 a4 aa a9 wvs/vron' JR. PIERCE ATTORNEY Patented Feb. 12, r 1952 ELECTRON GUN John R. Pierce, Millburn, N. .l'., asslgnor to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application July 7, 194 9, Serlal No. 103,448

Claims. (Q1. 313-338) This invention relates to electron guns and more particularly to electron guns for producin a plurality of electron streams and especially suitable for use in amplifiers of the type disclosed in the application Serial No. 38,928, filed July 15, 1948 of W. B. Hebenstreit and J. R. Pierce.

One general object of this invention is to improve electron guns for producing a plurality of electron beams. More specifically, objects of this vidual electron stream, the members or surfaces being in intimate thermal relation whereby all may be heated to the temperature requisite for copious emission by a single heater element, one member being heated directly and the other or others by radiation from the first.

In one specific construction illustrative of this invention, the electron gun comprisesa unitary assembly including three cylindrical cathode members mounted in closely spaced relation one within another, the cathode members having substantially concentric electron emissive coatings, and a single heater element encompassing the outermost of the cathode members.

The invention and the aforenoted and other features thereof will be understood more clearly and fully from the following detailed description with reference to the accompanying drawings in which:

Fig. 1 is a sectioned elevational view of an electron discharge device having a plurality of interacting electron beams generated in a gun constructed in accordance with one embodiment of this invention;

Fig. 21s a plan view of the gun of Fig. 1 taken along the line 22 of Fig. 1;

gated evacuated enclosing vessel [0 having at one end thereof a metallic portionv ll enclosing and supporting an electron gun structure I2 on a plurality of lead-in conductors, I3 sealed through glass beads M which in turn are sealed through apertures IS in the base l6. Sealed to the metallic portion I I is an elongated electron discharge space tube H, which may be of glass, having a stem H3 at its opposite end through which leadin conductors l9 and 20 supporting respectively a collar 22, forming a base for the output helix 23, and a collector electrode 24. The assembly 10 is surrounded by a solenoid 25 which produces an axial magnetic field for the purpose of focusing the electron beams of the gun l2.

The focused electron beams are controlled by an electromagnetic field traveling along a portion of the length of the discharge space in tube I! and fed to the device by means of a wave guide 26 which has a shorted termination 21. The guide carries a signal which is coupled to the input helix 28 by the extension of that helix 29 running parallel to the axis of the electron stream and mechanically supported by the collar 30. The signal traveling down the helix 28 effects one of the electron streams which in turn interacts with the adjacent stream in a manner set forth in the verse manner to that of the input, namely, the v electromagnetic field traveling down the electron discharge space inside the helix 23 is picked up by that helix and fed to the output wave guide 32 by the straight section 33 at the end of the helix.

, It is to be noted'thatthe input and output Fig. 3 is a sectioned elevational view of another embodiment of this invention suitable for incorporation into a discharge device of the type shown in Fig. 1; s

Fig. 4 is a plan view of the gun of Fig. 3 taken along the line 44 of Fig. 3;

fhelices 28 and 2 3 are connected by an electrically conductive sleeve 34 thereby imposing the direct-current collector potential on the ring 30 to provide an accelerating field for the electron gun.

In order to isolate the input and output signals of the device it is therefore necessary to effecftively terminate the ends of the helices 28 and 23 with their characteristic impedance, thereby, ineifect, providing an open circuit to the signal frequencies. This is done by coating the exterior of the tubular portion of the envelope I! with some loss material 2|, such as a colloidal suspension of graphite, in the area adjacent the ends of the helices.

The electron gun l2 as shown in Fig. 1 comprises three cathodes 4| and 42 formed by coating the ends of the central metal cylinder 43 and the two enclosing metal sleeves 44 and 45 aesassa a; g. with a material having good thermionic emission characteristics. These cathodes are supported on each other and the iead=in connectors i?) by -reiterates d6. li and which also provide electrical connections to the sleeves 65 and i6 and the cylinder 63 respectively, the strap as, which by means at the glass bead 56; is electrically isolated from the cathode sleeve 65, and ceramic spacers 62, for example rings, which center sleeve 6-3 in sleeve t and cylinder 63 in sleeve M. The inti= mate. mechanical relationship of the cathode bodies 43. 44 and 45 when supported in this manner enables high emission to be attained from each cathode without the necessity for individual heaters. Thus, in the gun of Fig. 1, one heater 55 which may be in the form of a helix of suitably insulated high resistance. wire mounted concentric with the sleeve 45 and enclosed in an annular compartment formed by auxiliary sleeve 56 on sleeve 45, heats the sleeve 45 directly and by radiant heat the adjacent sleeve 44 and cylinder 43 so that all are at a suillciently high temperature to provide copious thermionic emission from the surfaces 40, 4| and 42.

Electrically, the gun of Fig. l is arranged so thatthe outer and inner cathodes 40 and 42 are connected to the negative terminal of the battery 95 by means of lead 53, strap 46 and strap 48. The intermediate cathode 4| is held at a somewhat higher potential relative to the accelerating electrodes than the cathodes 40 and 42 by the .battery 95 connected thereto through the lead 54 and the strap 41 thereby producing a slower stream of electrons intermediate those streams from the cathodes 40 and 42.

An accelerating electrode 51 is mounted immediately ahead of the cathodes 40, H and 42 on a metallic ring 58 which in turn is secured to a metallic annulus 59 of Kovar or other metal which can be conveniently sealed to glass. This annulus is sealed between the tubular glass section 60 and the enlarged base portion SI of the tube I1, and serves as a conductor from the battery 62 through the lead 63 to the accelerating electrode. The collar 30, as pointed out heretofore, is held at the collector potential by the battery 64 which is connected to the collector leadin 20 and the collar lead-in H! by the parallel leads 66 and 61. Thus substantially all the acceleration of the electron beams due to the directcurrent potential of the batteries 95, 62 and 64 take splace in the space between the cathode and the ring 30.

While the embodiment of the gun of Fig. 1 produces three concentric electron streams, or two intermingled streams, traveling at difierent speeds down the length of the tube H, for some applications two concentric streams may be desirable. Figs. 3, 4, 5 and 6 disclose double cathodes Ior single heater electron guns suitable for incorporation into a device such as that shown in Fig. 1.

The cathode structure illustrated in Figs. 3 and 4 comprises a concentric metal sleeve 10 and metal cylinder H. the ends of which are coated with a suitable thermionic emissive material to produce cathode surfaces 12 and I3. Depending from the sleeve Ill and enclosing the helical heater I4 concentric therewith is a second metal sleeve 15. This sleeve in combination with the intimate relationship between the sleeve 10 and J provide suitable thermionic emission from both surfaces while employing only a single heater.

The accelerating electrode 76 and the heater and cathode leads are shown in schematic form in Fig. 3 it being understood that the assemblage could he supported in an envelope in a manner similar to the gun assembly lb of Fig. 1. This gun is arranged so that the inner beam is of higher speed than the outer beam by putting a higher potential dlfierential between the acceler ating electrode 16 and the cathode 13 than exists between the electrode and the cathode 12, this being done by placing batteries TI and 18 in series between the cathode l3 and electrode 16, and only battery 18 between cathode I2 and electrode 116. Battery 19 supplies power for the heater Hi.

The embodiment of Figs. 5 and 6 differs from the structure of Fig. 3 in that the cathodes are formed in a pair of coaxial cylindrical emissive surfaces 80 and 8|, one on the end or a central cylinder 82, and the other on the wall of the aperture 83 in the closed end of the double-walled sleeve 84, the outer wall 85 of which forms the housing for the heater 86. Here again, the battery 81 provides the power for the heater. and the batteries 88 and 89 establish the accelerating potentials between the accelerating electrode 90 and the cathodes.

What is claimed is:

1. An electron gun comprising a first cathode having an annular end wall and spaced inner and outer cylindrical members extending from said wall, an electron emissive coating on said first cathode, a heater element between said inner and outer members, and a second cathode heated solely by radiation from said first cathode and having an electron emissive end portion adjacent said end wall, said second cathode being mounted in proximity to and encompassed by said inner member.

2. An electron gun comprising a first cathode having an annular end wall and spaced inner and outer cylindrical members extending from said wall, an electron emissive coating on said end wall, a heater element between said inner and outer members, a second cathode heated solely by radiation from said first cathode and having an electron emissive end portion adjacent said end wall. and a third cathode mounted within and heated solely by radiation from said second cathode and having an electron emissive end portion adjacent said second emissive surface, said second cathode being mounted in proximity to and encompassed by said inner member and said third cathode being mounted in proximity to and encompassed by said second cathode.

3. An electron gun comprising a plurality of closely adjacent cylindrical cathode members mounted one within another, said members having substantially coplanar faces at one end thereof, electron emissive coatings upon said faces, and means for heating said coatings consisting of a heater element encompassing the outermost of said members.

4. An electron gun comprising a pair of cylindrical cathode members arranged in intimate heat transfer relationship and mounted one within the other in spaced substantially coaxial relation, insulating spacers between the adjacent cathode members and adjacent the end of the inner cathode member, electron emissive coatings at one end of each of said members, the coated ends being in proximity to one another, a single heater filament for the cathode members, said filament encompassing the outermost cathode member, and heat shield means encompassing said filament.

5. An electron gun comprising a first metallic cathode member having a cylindrical recess in one end thereof, an electron emissive coating on the cylindrical wall of said recess, a second metallic cathode member disposed about said first cathode member and having at one end thereof a cylindrical aperture, opposite, coaxial with and of greater diameter than said recess, an electron emissive coating on the cylindrical bounding wall of said aperture, and a single means for heating said cathode members.

JOHN R. PIERCE.

REFERENCES CITED The following references are of record in the file of this patent:

Number 8 UNITED STATES PATENTS Name Date Macksoud Sept. 10, 1929 Danforth Jan. 22, 1935 Ruben Feb. 12, 1935 Stansbury Sept. 17, 1935 Sukumlyn Mar. 31, 1936 Bruche Apr. 21, 1936 Farnsworth Nov. 23, 1937 Llewellyn Mar. 2, 1943 Hansen et a1 Aug. 27, 1946 Samuel Oct. 15, 1946 Smith Oct. 26, 1948 

